The distance of an object measured from a reference point, whereat the distance measuring unit is positioned with an appropriate measurement stop, is typically measured with such generic distance measuring units. Such distance measuring units can, for example, be designed as laser measuring units, as ultrasonic measuring units or also as high frequency, respectively radar measuring units. In all of the above cases, the distance is determined by direct, respectively indirect, measurement of the elapsed time of a modulated signal sent out from the measuring unit, which is reflected off an object to be measured and subsequently received by the measuring unit.
A distance measuring unit, which can be used for different measuring tasks, is known from the German patent DE 43 163 48 E1. The measuring unit can therefore, for example, be positioned on the reference surface for the frequently encountered application of a measurement starting at an interior surface, as, for example, an inner wall, on the back side of a floor or a ceiling, i.e. with a stop surface facing away from the object. In the event that a measurement is being taken starting at an outer edge, the known distance measuring unit can be positioned on the reference surface with its front side, i.e. with a stop surface facing toward the object, in the direction towards the object to be measured. In the case of the device from the German patent DE 43 163 48 A1, the front and the back side of the unit are configured parallel to each other.
Depending upon the application, either the front side or the back side of the distance measuring unit is defined as the unit-sided reference point, respectively zero point, of the distance measurement.
An electronic distance measuring unit with a transmitter for a measuring beam and a receiver for a returning, reflected beam as well as an evaluation unit for ascertaining the distance from the measuring unit to the point of reflection is known from the German patent DE 296 15 514 U1. Said unit has in each case a measuring spatula on two surfaces, which are situated parallel opposite one another, of its housing, which is configured to have a substantially cuboid form. Said spatulas, which are fastened on the unit housing as to move forwards and backwards and are fixed in guides on both sides of said housing, can on the one hand be retracted to the front face of the unit, respectively can be pulled out in another stable end position to an exactly predefined distance. The position of the measuring spatulas when pulled out is automatically determined by pushbutton switches present in the guides of these spatulas or in the housing wall of the measuring unit and is transmitted to an evaluation unit of the electronic distance measuring unit.
An optoelectronic laser distance measuring unit is known from the German patent DE 100 55 510 A1. Said unit has a planar measurement stop, which can be pulled out of the housing, on its housing rear side facing away from the measuring direction.